<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>左右固定，中间自适应布局</title>
    <style>
      body {
        margin: 0;
        padding: 0;
      }
      .item {
        box-sizing: border-box;
        height: 600px;
        border: 1px solid #f00;
      }
      .b1 {
        width: 200px;
        background: #87ceeb;
        position: fixed;
        top: 0;
        left: 0;
      }
      .b3 {
        width: 200px;
        background: #ffd700;
        position: fixed;
        top: 0;
        right: 0;
      }
      .b2 {
        background: #ff6347;
        margin: 0 210px;
      }
    </style>
  </head>
  <body>
    <div class="box">
      <div class="item b1"></div>
      <div class="item b2"></div>
      <div class="item b3"></div>
    </div>
  </body>
</html>
